1. Field of the Invention
The present invention is directed to a rotor blade for a flow machine, in particular a steam turbine, comprising an insertion root with a plurality of fingers having radially outer first portions and radially inner second portions whose axial extension is shorter than that of the outer portions, and to a flow machine, particularly a steam turbine, having rotor blades of this kind.
2. Related Art
At present, besides rotor blades that are fixedly connected, e.g., welded, to the rotor of the flow machine, rotor blades with fir-tree turbine blade roots and insertion roots are commonly used, particularly in steam turbines. For example, Dubbel, Taschenbuch für den Maschinenbau, 20th edition, page R 67, shows a rotor blade for a steam turbine having a three-fingered insertion root, wherein the individual fingers have a shoulder on either axial side such that the fingers have a radially outer first portion and a radially inner second portion whose axial extension is shorter than that of the outer first portion.
Insertion roots of this type must withstand high stresses in operation. For one, large centrifugal forces acting in radial direction occur particularly at higher rotor speeds. Further, the medium which flows around, and is deflected by, the rotor blades, e.g., the steam which performs the work and is expanded in a steam turbine, exerts forces in axial direction and circumferential direction on the rotor blades which must be supported in the insertion roots.